Multiple material bumper beam

BACKGROUND OF THE INVENTION

00011. Field of the Invention

0002The present invention relates to a bumper assembly for a motor vehicle, and more particularly to a bumper beam having multiple material properties.

00032. Description of the Related Art

0004Automotive designers are continually trying to balance the need for lightweight, fuel efficient automobiles with safety standards and regulations imposed by the government and insurance companies. One such automotive component subject to heavy regulation is bumper assemblies with regard to crash safety standards. The bumper assembly is traditionally comprised of a bumper beam made of a metallic material with the requisite strength to conform to governmental standards for low and high speed crashes. Often, the strong metallic beam is heavy and adds significant weight to the vehicle thereby reducing fuel efficiency. There is a need in the automotive industry to develop a bumper assembly having a bumper beam with an increased strength to weight ratio by lowering the overall weight of the bumper assembly. The improved bumper assembly must still be strong enough to provide excellent performance in high speed and low speed crashes.

0005Furthermore, automotive manufacturers desire components that are affordable and easy to produce in a mass production operation. Traditional bumper assemblies are roll-formed whereby a flat steel strip extends through a series of rollers to shape the steel into a desired form. Complex bumper beam designs, while providing the necessary strength to conform to safety standards, add to the time and cost of the manufacturing process. There is a need in the automotive industry to produce a bumper beam that provides strength adequate to conform to safety standards, lightweight to improve fuel efficiency and simple to manufacture.

SUMMARY OF THE INVENTION

0006The inventors of the present invention have recognized these and other problems associated with the traditional bumper beams described above. To this end, the inventors have developed a bumper beam that weighs less while maintaining high quality standards related to impact or crash testing.

0007Specifically, the invention comprises a bumper beam having a first portion comprising a first material, and a second portion comprising a second material. The first material has different material properties than the second material.

BRIEF DESCRIPTION OF THE DRAWINGS

0008In the drawings:

0009<figref idref="DRAWINGS">FIG. 1</figref> is a perspective view of a bumper beam of the present invention;

0010<figref idref="DRAWINGS">FIG. 2</figref> is a cross-sectional view of a first embodiment of the bumper beam of the present invention taken along the line <b>2</b>—<b>2</b> of <figref idref="DRAWINGS">FIG. 1</figref>;

0011<figref idref="DRAWINGS">FIG. 3</figref> is a perspective view of a second embodiment of a bumper beam of the present invention;

0012<figref idref="DRAWINGS">FIG. 4</figref> is a cross-sectional view of the second embodiment of the bumper beam of the present invention taken along the line <b>4</b>—<b>4</b> of <figref idref="DRAWINGS">FIG. 3</figref>; and

0013<figref idref="DRAWINGS">FIG. 5</figref> is a cross-sectional view of an alternate embodiment of the bumper beam of <figref idref="DRAWINGS">FIG. 2</figref> in which the first portion has a different thickness than the second portion.

DESCRIPTION OF THE PREFERRED EMBODIMENT

0014Referring to <figref idref="DRAWINGS">FIGS. 1 and 3</figref>, a bumper beam, generally referred at <b>10</b>, is shown according to an embodiment of the invention. The bumper beam <b>10</b> is an elongated beam having a first portion <b>12</b> and a second portion <b>14</b>. In one embodiment, the second portion <b>14</b> is fixedly attached to a vehicle (not shown) by traditional techniques, such as fasteners, bracket assemblies, or the like. The first portion <b>12</b> extends outwardly from the vehicle and is usually first to contact an external object (not shown) during a crash. The positions of the first portion <b>12</b> and second portion <b>14</b> are merely illustrative. Alternatively, the second portion <b>14</b> may be attached to the vehicle while the first portion <b>12</b> extends outwardly from the vehicle.

0015One aspect of the invention is that the first portion <b>12</b> and the second portion <b>14</b> are made from different materials, such as a first material and a second material, respectively. By way of example, the first portion <b>12</b> is made from the first material that is generally higher strength (tensile strength or yield strength) than the second material of the second portion <b>14</b>. It has been found that forming the first portion <b>12</b> with the first material having a greater strength enables the bumper beam <b>10</b> to greater withstand the forces generated on the bumper beam <b>10</b> during a crash, as compared to a bumper beam made of a single material having a lesser strength than the first material. The second portion <b>14</b> is made from the second material having a lesser strength (tensile strength or yield strength) than the first material, but weighing less or the same as the first material. It has been found that the combination of the higher strength first material and the lighter or equal weight second material provides a bumper beam <b>10</b> with an increased or higher strength to weight ratio, as compared with traditional bumper assemblies made of a single material. The increased strength to weight ratio provides a bumper beam that conforms to governmental standards regarding high and low speed crashes, while also improving fuel efficiency of the vehicle. As a further example, the second material of the second portion <b>14</b> may be of generally higher strength (tensile strength or yield strength) than the first material of the first portion <b>12</b> while the first material weighs less than or equal to the second material. Any combination of materials having different material properties that results in an increased or higher strength to weight ratio of the bumper beam is contemplated by the present invention.

0016In addition, the first material can be of a different gauge than the second material. For example, the first material of the first portion <b>12</b> can have a lesser thickness than the second material of the second portion <b>14</b> because the first material comprises a higher strength material than the second material, as shown in FIG. <b>5</b>. In contrast, if the second material has a higher strength than the first material, then the second material may have a lesser thickness than the first material.

0017In an illustrated embodiment of the invention, the first portion <b>12</b> comprises martensitic steel. It has been found that martensitic steel provides very high structural strengths, for example, up to 1500 MPa ultimate tensile strengths, while still having remarkable formability. However, it will be appreciated that the invention is not limited by the specific material for the first material of the first portion <b>12</b>, and that the invention can be practiced with other suitable materials that provide the strength needed for bumper assemblies.

0018Referring to <figref idref="DRAWINGS">FIG. 2</figref>, a cross-sectional view of a first embodiment of the bumper beam <b>10</b> is shown. As seen in <figref idref="DRAWINGS">FIG. 2</figref>, the first portion <b>12</b> is generally C-shaped in cross-section and includes a back <b>16</b> and two legs <b>18</b>. The legs <b>18</b> extend generally orthogonally from the back <b>16</b> at one or more bending portions <b>20</b>.

0019Referring to <figref idref="DRAWINGS">FIG. 4</figref>, a cross-sectional view of a second embodiment of the bumper beam <b>10</b> is shown. As seen in <figref idref="DRAWINGS">FIG. 4</figref>, the first portion <b>12</b> is generally C-shaped in cross-section and includes a back <b>32</b> and two legs <b>34</b>. The legs <b>34</b> extend generally orthongonally from the back <b>32</b> at one or more of the bending portions <b>20</b>.

0020In the illustrated embodiments of the invention, the second portion <b>14</b> comprises a dual-phase, multiphase, complex-phase or transformation induced plastic (TRIP) steel. One such material determined suitable for the second portion <b>14</b> of the bumper beam <b>10</b> is currently marketed under the trade name DI-Form 140T. DI-Form 140T is commercially available from Ispat Inland Inc. of East Chicago, Ind. (www.ispat.com). DI-Form 140T has an ultimate tensile strength of approximately 965 MPa. Although the second material of the second portion <b>14</b> is generally of a lower strength than the first material of the first portion <b>12</b>, the second material of the second portion <b>14</b> weighs less than or equal to the first material of the first portion <b>12</b>. It will be appreciated that the invention is not limited by the specific material used for the second portion <b>14</b>, and that any material suitable for providing the necessary strength of the bumper assembly, while reducing the weight of the assembly, is acceptable for the second material of the second portion <b>14</b>.

0021Referring to the first embodiment in <figref idref="DRAWINGS">FIG. 2</figref>, the second portion <b>14</b> includes two generally C-shaped sections <b>21</b>, <b>23</b> integrally joined together by a connecting segment <b>22</b>. Similar to the C-shaped first portion <b>12</b>, each C-shaped section <b>21</b>, <b>23</b> of the second portion <b>14</b> includes a back <b>26</b> and two legs <b>24</b>, <b>28</b>. One of the legs <b>24</b> is generally orthogonal to the back <b>26</b>, while the second leg <b>28</b> extends angularly from the back <b>26</b>. In the illustrated embodiment, the second leg <b>28</b> extends at an acute angle with respect to the back <b>26</b>. Each C-shaped section <b>21</b>, <b>23</b> includes one or more bending portions <b>20</b>.

0022Referring to the second embodiment in <figref idref="DRAWINGS">FIG. 4</figref>, the second portion <b>14</b> includes two generally C-shaped sections <b>21</b>, <b>23</b> integrally joined to each other. Each C-shaped section of the second embodiment includes a back <b>38</b> and two legs <b>36</b>, <b>40</b>. Both legs <b>36</b>, <b>40</b> extend generally orthogonally from the back <b>38</b> at one or more of the bending portions <b>20</b>. The legs <b>40</b> of each C-shaped section are integral to form one extended segment between the backs <b>38</b> of each C-shaped section. The C-shaped sections are symmetrical about a longitudinal axis, A, whereby the axis A, is midway between the backs <b>38</b>.

0023The first portion <b>12</b> and the second portion <b>14</b> of both embodiments are fixedly attached to each other at one or more locations, indicated at <b>30</b>, such as by welding, or the like. In the first illustrated embodiment, the first portion <b>12</b> and the second portion <b>14</b> are welded to each other at each of the legs <b>18</b> of the first portion <b>12</b> and each of the legs <b>24</b> of the second portion <b>14</b>. Further, the connecting segment <b>22</b> is welded to the back <b>16</b> of the first portion <b>12</b> at a location <b>30</b> along the longitudinal axis, A, of the bumper beam <b>10</b>. Finally, the bending portions <b>20</b> formed between the back <b>26</b> and the legs <b>28</b> are welded to each other along the longitudinal axis, A, of the bumper beam <b>10</b>. As can be seen in <figref idref="DRAWINGS">FIG. 2</figref>, the bumper beam <b>10</b> is generally mirror symmetric with respect to the longitudinal axis, A. As a result, the location <b>30</b> at which the back <b>16</b> is welded to the connecting section <b>22</b> and the location <b>30</b> at which the bending portions <b>20</b> formed between the back <b>26</b> and the legs <b>28</b> are welded lie along a midpoint between the legs <b>18</b> of the first portion <b>12</b>.

0024In the second embodiment the first portion <b>12</b> and second portion <b>14</b> are welded to each other at each of the legs <b>34</b> of the first portion <b>12</b> and the bending portions at each of the legs <b>36</b> of the second portion. Further, the back <b>32</b> of the first portion <b>12</b> is welded to the legs <b>40</b> of the second portion <b>14</b> along the axis, A, of the bumper beam <b>10</b>.

0025It will be appreciated that the locations <b>30</b> of the welds to join the first portion <b>12</b> and the second portion <b>14</b> are only illustrative, and the weld locations <b>30</b> may be positioned anywhere suitable for fixedly attaching the first portion <b>12</b> and the second portion <b>14</b>. Furthermore, other techniques known in the art for attaching the second portion <b>14</b> and the first portion <b>12</b> are also within the scope of the invention.

0026The cross-sectional configurations of the bumper beam <b>10</b> shown in the accompanying figures are only two examples of a bumper assembly that provides an increased strength to weight ratio as compared to conventional bumper assembly designs. Any cross-sectional configuration that incorporates two different materials is also contemplated by this invention. The configuration of the bumper beam <b>10</b>, as shown, positions the higher strength material only where necessary to absorb forces during a crash. Utilizing the higher strength first material only where necessary allows the remainder of the bumper beam <b>10</b> to be manufactured of a lower strength, lighter second material.

0027Furthermore, the overall shape of the bumper beam <b>10</b>, as shown in the figures, helps to provide additional stiffness to the beam. For example, the cross-sectional configuration of the first portion <b>12</b> being generally C-shaped along with the cross-sectional configuration of the second portion <b>14</b> with two C-shaped sections provides additional stiffness and helps the bumper beam <b>10</b> withstand forces during a crash. One benefit of the cross-sectional configuration of the invention is that the invention may eliminate the need for an energy absorber commonly found in traditional bumper assemblies.

0028Finally, the bumper beam <b>10</b> of the present invention is also simple to manufacture. As with traditional bumper assemblies, the bumper beam <b>10</b> is roll-formed. The first portion <b>12</b> and the second portion <b>14</b> are welded together and then roll-formed. Once formed, the first portion <b>12</b> and second portion <b>14</b> are then welded together within the assembly line at additional locations. The two-material design of the bumper assembly <b>10</b> of the invention provides the opportunity for in-line welding of the first portion <b>12</b> and the second portion <b>14</b> to form the bumper beam <b>10</b> and reduces extra material handling that may result from using two different materials.

0029While the invention has been specifically described in connection with certain specific embodiments thereof, it is to be understood that this is by way of illustration and not of limitation, and the scope of the appended claims should be construed as broadly as the prior art will permit.